Autoclave



Feb. 23, 1943. v. l.. KING ETAL AUTOCLAVE Filed Oct. 23, 1940 3Sheets-Sheet 1 INVENTORS /r//VG 'I El!!! l l Feb. 23, 1943. v. l.. KINGETAL' AUTOCLAVE Filed oct. 25, 1940 3 Sheets-Sheet- 2 n n l 1 u l n l Il |I v Feb. 23, 1943. v L, K1N@ HAL 2,312,217

AUTOCLVE Filed Oct. 23, 1940 3 Sheets-Sheet 3 INVENTORS.'

4 7 rafa/wry Paten-,ted Feb. 23,1943

Victor L. KinnBound Brook, Carl E. Menaing,

Somerville, and Don H. W. Felch. Plainiield, N. J., assignors toAmerican Oyanamid Company, New York, N. Y., a corporation ofl Mime yApplication October 23, 1940, Serial No. 382,333

4 Claims. (Cl. 23-290) This invention relates to improvements inautoclaves such as are used in carrying out chemical reactions underpressure. In its more specific aspects, the invention relates to a newand improved type of autoclave designed especially for treating slurrlescontaining liquids mixed with solid particles. Objects of the inventionare to provide an autoclave capable of producing high yields ofconversion products -of good quality by means of aclosely regulatedtemperature control, to permit a shortened cycle of operations byenabling rapid charging and discharging of the autoclave, and to providea type of heating and/or cooling means within the autoclave that willnot cause settling out, bridging over, or caking of the solid particlescontained in slurrles undergoing treatment.

Many chemical reactions that must be carried out under high pressuresinvolve the treatment of suspensions or slurrles of solids in liquids.Thus, for example, beta-amino-anthraquinone is prepared from asuspensionof chloranthraquinone in ammonium hydroxide liquor; 2.6-

diamino-anthraquinone is prepared from anthra-V quinone2.6disulfonicacid; and tetra-aminoanthraquinone is prepared fromtetrachloranthraquinone and aqueous ammonia. Another type of reaction isone in which the solution undergoing treatment is a relatively clearliquid but the reaction product is a crystalline or amorphous slurry,such as is obtained by the conversion of a solution of cyanamide ordicyandiamide in liquid ammonia into melamine. In this latter case theslurry is the product of the reaction, but the problems involved are thesame.

Processes of the above and similar types must be carried out in pressurevessels capable of withstanding both high pressures and `hightemperatures. Under these circumstances the provision of satisfactoryagitators that will'maintain the autoclave charge in a-fluid conditionwith adequate provision for temperature regulation has remainedajdiilicult problem. The design of an autoclavecapable of withstandingthese -high pressures and yet operating to produce high yields ofconversion products in a minimum of operating time and without cloggingor caking constitutes a further and more specific object of ourinvention.

We have found that the course of the above and similar reactions can beclosely controlled within an autoclave capable of withstanding highpressures by the provision of a ring of vertical heating or coolingelements over which the slurry constituting the reaction mixture or thereaction product is recirculated in a vertical circuit. By continuouslyrecirculating a stream of the reaction mixture in this manner we findthat the reaction is maintained at a uniform rate throughout all partsof even a large autoclave, so that local temperature differences areavoided and a uniform operation is obtained. Not only does this resultin an improvement of the quality of the product from a single autoclavecharge, but successive batches prepared in the same autoclave will havesubstantially the same analysis so that the daily output of the plant ismade more uniform. f

'I'he details of a preferred modification of our invention, and of theprocess inherent in its operation, will be illustrated in the accompany`ing drawings, in which: 1

Fig. 1 is an assembly drawing with parts broken broken away showing theautoclave, recirculating mechanism and lubricating means;

Fig. 2 is an. enlarged rvertical section of the lower part of Fig. 1with parts shown in elevation and parts broken away;

Fig. 3 is4 an enlarged detail' of a lower part of the annular heatingbaille of the autoclave;

Fig. 4 is a plan view of the portion of the annular baille shown inelevation in Fig. 3 with one pipe extended to show the spiderattachment; and

Fig. 5 is a plane development of the baille showing'the assembly of theheating tubes vand the spacing of the orlces in the banles. y

Referring to Fig. 1, the autoclave which is designated generally byreference numeral i,

comprises preferably a cylindrical shell or body` member 2 provided withupper and lower heads 3 and l respectively.: As is shown in greaterdetail in Fig. 2, the bottom` head l is fitted inside the outer shell 2and retained by an annular clamping ring li fastened by stud bolts 6,and a similar construction is used forsecuring the top headl of theautoclave.

The autoclave is preferably charged and discharged through an orifice 1which is bored through the bottom head 4 and which connects f with apipe 8 having a branch pipe 9 and a valve i0. By this means theautoclave may be charged through the valve i0 with apreformedsusperrsion of the reaction mixture, such as a` slurry ofbeta-chloranthraquinone in aqua ammonia, and after the heating cycle iscompletedv the slurry may be discharged'through the pipe 9 and a secondcharge of the reaction mixture admitted immediately while the rautoclaveis still hot.

Mounted within the autoclave centrally of the shell 2 and spaced fromthe top and bottom heads I and l is an annular heating or cooling baiiieII which operates in accordance with'the present invention, both tosupply heat to or to cool the reaction mixture therein and to maintain arecirculatlng stream thereof during a heating or cooling cycle. As isshown in greater detail in Figs. 3, 4 and 5 of the drawings, this bameis made up of a plurality offsubstantially vertical heating or coolingtubes I2 and welded at either end to upper and lower annular headers Iland Il. Flat metal'strips Il and Ii-are welded longitudinally to each ofthe heating tubes I2 on opposite sides thereof, the positions of thesestrips being such that the outer strip Il of one tube makes a closesliding fit with the inner strip I6 oi.' the adjacent tube to allow forexpansion or contraction upon heating or cool.

ing. 'I'he vertical tubes I2 and the strips' Il and I6 form a continuousannular wall having the headers I3 and Il at the top and bottom thereofand the vertical tubes I2 extending between the headers and constitutinga part of the wall. High: pressure steam or other suitable temperatureregulating medium may be supplied to the upper header I2 through inletpipel I1 while exhaust steam and condensate are withdrawn from the lowerheader I4 through the pipe I2. In cooling the autoclave a cooling mediumsuch as water is preferably introduced through the pipe I8 andvwithdrawn through the pipe I1. Each of the pipes I1- and I8 passesthrough the bottom head 4 of the autoclave through suitable holes I9 and20 bored therein.

In Aorder to control positively the speed and degree of recirculation ofthe reaction mixture within the autoclave, a recirculating means is`provided in the form of a propeller 2|. This propeller is mounted onA ahollow, water-cooled drive shaft 22 which passes through a bushing 2l, abearing 42, a stumng box 2l and a grease receiverv 25, being ilnallysupported by a thrustbearing suitably mounted in a housing 28. Below thenearing it is connected with a set of speed reducing bevel gears whichare driven throigh the shaft 21 and pulley A28 by the mov tory 9i`During the heating cycle the propeller 2l is lation upwardly throughthe annular outer passage formed between the annular baille II and theshell 2 of the autoclave and downwardly through the ring or cylinderformed by the baille itself. Y. In order to insure a uniform path oftravel under conditions where the liquid level does not extend above theupper ring 22, as during charging and discharging of the autoclave,orifices 20 are provided lin the strips IB and It that make up the bamestructure. These orifices are spaced alongl the line of a helix drawnaround the cylindrical baille Il, as shown in Fig.` of the drawings, andthey therefore permit a continuous recirculation of the reactionmixture, or of the slurry which is the final reaction product,independently of the amount of liquid present in the autoclave. Stagnantheating while charging a hot autoclave and the resulting c'aking duringthe charging and discharging periods are thereby avoided, and this isjan important advantage of the invention.

The temperature conditions within the autoclave during the heating cycleare most readily followed by the provision of a movable thermocouplelocated in a thermocouple well (not shown) in the center of the heatingbaille II.

This well is inserted through a packing gland located in the top head lof the autoclave. and

' in order to support and retain its lower portion in position when thepropeller 2| is in operationa supporting funnel-'2| is provided. Thisfunnel has a-lower annular'portion 22 which is supported by a spider 22attached to three of the vibratie f1 iis Because of the high pressureand high temperature conditions existing in thev autoclave,`

the problem of driving the propeller 2| is of special importance. Inorder to maintain a recirculation of the slurry at the speeds necessarytc prevent settling and caking a powerful drive is needed for thepropeller 2l, and special means to support and lubricate the drive shaft22 are provided by our invention. i.

As is illustrated in Fig. 2 of the drawings.. a bore 2B is provided inthe drive shaft 22 extend@ ing from its lower end as'far as the bushing22. A water tight connection is made at the lower end of the shaft witha drain pipe 21, and with in this pipe there is inserted a' small waterpipe 22 which extends through the drive shaft 22 vto the upper end ofthev bore. By maintaininga ilow of cooling water upwardly through thepipe stantially higher than autoclave pressure would result in theleakage of oil or grease into the autoclave which would contaminate theproduct. Inasmuch as there may be a considerable variation in theautoclave pressure during the charg ing and discharging periods as wellas during the heating cycle it is evident that .pressurelubricationunder a constant pressure cannot .be resorted to.

We provide a successful solution to the problem of variable pressurelubrication by using the autoclave itself as a generator of pressure forthe lubricating oilorgrease.` Ii'or this purpose we provide an oilreservoir 40 which is located a suillcient distance above the normalliquid level in the autoclave to supply a hydrostatic head ca'- pable ofproducing a satisfactory flow of oil into the bearing. An oil line 4Iconnects this reser voir 40 with a grease lantern 42 located in thehousing Il adjacent the stuffing box 2l. A pipe 4l extending through thetop head 2 of the autoclave provides communication between the interiorof the' autoclave and the top of the oil reservoir 4l, so that thepressure generated in the autoclave at any time during the heatingcycle'is transmitted to the surface of the lubricating oil. The resultof this construction is that the .pressure in the autoclave is balancedby a similar pressure on the Ysurface of the oil, and the new of oil-into the lantern 42 is always under a relatively constant hydrostaticpressure. "i

From the foregoing it will be seen that the preferred modification ofthe invention which has been described is one that, accomplishes all theobjects thereof.' During the charging and discharging periods the slurryundergoing treatment is recirculated through a vertical circuit, passingupwardly in the annular space between the baille structure I I and theshell 2 of the autoclave, through the orices 30, and downwardly throughthe annular passage formed by the ring of heating tubes I2. When theautoclave is lled to its normal operating level the same direction ofrecirculation is maintained, but the greater part of the flow passesover the top of the upper header I3. In all cases, however, therecirculation is defined by substantially vertical surfaces, as theoriilces 30 are formed in relatively thin metal strips and there are noledges or shelves on l which deposits may form. By supplying a coolingor heating medium such as high pressure l steam to the ring of verticaltemperature regulating elements I2 the proper degree of heating orcooling of the reaction mixture is maintained throughout the entirecycle and a close temperature regulation is thereby maintained at alltimes. A shortened cycle of operation and greater uniformity in thequality of the product are thereby obtained.

`The operation of the autoclave of our invention will now beillustrated: In the manufacture of melamine a solution consisting ofequal parts by Weight of cyanamide or dicyandiamide, liquid ammonia, anda diluent such as methanol may be employed, while in the manufacture ofa guanidine salt such as guanidine nitrate an equivalentquantity of thecorresponding ammonium salt such as ammonium nitrate is added to thismixture. The charge is introduced into the autoclave through the valve Iand pipe 8, and the solution is recirculated by operation of thepropeller 2|. `By reason of 'the vertical baille structure II thesolution ls caused to travel upwardly through the annulus formed betweenthe ring of flanged heating tubes I2 and the shell 2 of the autoclaveand downwardly within the ring of tubes. During the heating cycle themain ilow of liquid is over the top of the header I3, although at leasta part of the liquid passes through the oriilces 3U, but during thedischarge period practically all the lateral ilow is through theseorices.

The vertical heating tubes I2 are preferably maintained at a temperatureof' 10G-200 C. throughout the heating cycle,' and underthese conditionsa part of the cyanamide or dicyandiamide first reacts with the ammoniato form guanidine according to the following reactions:

'I'he guanidine then combines with more of the starting material to formmelamine with regeneration of the ammonia by the reactions If anammonium salt is present such as ammonium nitrate the reactions 3 and 4are inhibited as the acid radical of the ammonium salt serves to bindthe guanidine as a stable guanidine salt and it is no longer free tocombine with fur- \ture centrally located therein, said baille structurecomprising an upper header, a lower header and a ring of, vertical tubesprovided with overlapping flanges mounted between said headers, meansfor maintaininga recirculating flow of a fluid reaction mixturedownwardly within the ring formed by said tubes and flanges and upwardlyoutside said ring, and means for supplying a temperature regulatingmedium to saidv baille structure.

2. An autoclave comprising in combination a cylindricalpressure-resisting shell and an annular baille structure centrallylocated therein having vertical temperature regulating elements, saidbaille being spaced from the walls of said shell to provide a centralpassage and an outer annular baille, orics of substantial width butsmall area spaced in the sides of said baille to permitv the i'low ofliquid therethrough, means for maintaining a recirculating flow of afluid reaction mixture upwardly through said annular passage anddownwardly through said central passage, and means for supplying atemperature regulating medium to said temperature regulating elements.

3. An autoclave comprising in combination an outer cylindricalpressure-resisting shell and a cylindrical baille centrally locatedtherein, said baille comprising a continuous annular wall having headersat the top and bottom thereof and vertical tubes extending between saidheaders and constituting part of said wall, :said baille ibeing soconstructed and arranged as to have no horizontal ledges or crevices onwhich solid material may lodge, means for supplying a temperatureregulating medium to said baille, and means for maintaining arecirculating flow of a uid reaction mixture through the center of said`A baille and over the exterior surface thereof.

4. An autoclave comprising in combination an outer cylindricalpressure-resisting shell and a cylindrical baille centrally locatedtherein, said baille comprising a continuous annular wall having headersat the top and bottom thereof and vertical tubes extending between saidheaders and constituting part of said wall, said baille being soconstructed and arranged as to have no horizontal ledges or crevices onwhich solid material may lodge, means for supplying a temperatureregulating medium to said baille, and a propeller below said bailleadapted upon rotation to recirculate a fluid within the autoclaveupwardly through the center of lsaid baille and downwardly over theexterior surface thereof.

vIc'roR L. KING. CARL E. MENSING. DON H. W. FrmcH.

